The present invention relates to a spacer for retaining and fixing elongated fuel rods in a bundle arranged in a fuel box for a boiling-water reactor (BWR) or directly in the core for a pressurized-water reactor (PWR). The bundle is traversed in its longitudinal direction by a coolant. The spacers contain a number of cells for mutually fixing the fuel rods and are surrounded by an outer frame. This is normally formed from a first band, standing on edge, which may possibly be extended in the flow direction of the coolant by a skirt arranged on the upstream side of the spacer. To prevent the bundle from getting stuck when being inserted into a fuel box or into the core of a pressurized-water reactor, all the spacers have been provided with so-called guiding tabs. In known devices such tabs are formed from flaps or lugs extending from the spacer frame or the upstream edge of the skirt, these flaps being bent towards the centre of the spacer around a folding axis coinciding with the edge, that is, an axis perpendicular to the flow direction. This means that the flaps will present a large part of its side surface across the flow direction of the coolant. This, in turn, means that the flow resistance of the spacer is considerably increased, which, of course, is a drawback. In addition, the guiding tabs which are provided on the lower edge of the frame conduct the coolant away from the fuel rods and may thus deteriorate the cooling.
The present invention relates to an embodiment of the guiding tabs which eliminates the above-mentioned drawbacks. According to the invention, a guiding tab is formed from a plate flap or the like, the plane of which is arranged in parallel with the flow direction of the coolant and one side edge of which slantingly extends from the first band or skirt edge in an upstream direction towards the centre of the spacer. In this way, only the cross-sectional area of the plate flap perpendicular to the plane of the plate and the flow direction will constitute an obstacle to the flow of the coolant through the bundle. The reason for this is that the side surface of the plate flap will be parallel to the flow direction and thus not give rise to any flow resistance, nor will it control the coolant away from the fuel rods.
The invention will be most readily understood with reference to the accompanying drawings.